The progressive lung damage in cystic fibrosis (CF) arises from characteristic bacterial colonization with Pseudomonas aeruginosa being central After initial infection then colonization with wild-type strains, conversion of P. aeruginosa to the mucoid phenotype in the CF host occurs, increasing bacterial resistance to antibiotics and inflammatory lung damage, and causing declining pulmonary function and prognosis. There remains an unmet need for rapid, non-invasive diagnostic analysis of lung P. aeruginosa presence, burden and mucoid status. Such a diagnostic would enable real-time monitoring of infection, and also significantly improve CF management, that currently relies upon indirect measures such as lung function and culture of expectorated sputum (that is variable, samples only a part of the lung, not applicable to younger patients) or broncoalveolar lavage (that is invasive and unsuitable for repetitive use). We show that several isotopically labeled substrates can be uniquely converted by P. aeruginosa to volatile exhalable labeled gasses, in ways that depend upon bacterial phenotype. We therefore hypothesize that We can use P. aeruginosa-specific metabolism of stable isotopically-labeled compounds to exhaled gasses to determine lung infection, bacterial load, biofilm growth and mucoid status However, before we move to a translational clinical trial, we need to test our hypothesis, delineate the typical ratios of labeled volatiles in wild-type, biofilm and mucoid strains, and also demonstrate effectiveness in an animal model of CF lung infection with P. aeruginosa. We will therefore perform these aims: Specific Aim 1 Demonstrate and develop use of isotope ratio mass spectrometry to measure isotopically labeled gasses from denitrification, cyanide synthase and urease activities in P. aeruginosa in vitro. Specific Aim 2 Delineate the range of ratios of urease to cyanide synthase/denitrification products for non- mucoid and mucoid P. aeruginosa strains in vitro growing planktonically and in biofilms. Specific Aim 3 Demonstrate effectiveness of this diagnostic approach in mice with mucoid and non-mucoid P. aeruginosa lung infection. Successful completion of this preclinical stage would be followed by formulation work on an inhaled dosage form, and Phase 1 clinical trial. PUBLIC HEALTH RELEVANCE: Cystic fibrosis is a high-prevalence, life shortening genetic disease, with much of the lung damage coming from infection with P. aeruginosa. Yet, the clinical tools to monitor for P. aeruginosa presence, burden &phenotype, so that the infection can be actively and pro-actively managed are not suitable or available. We propose to test the potential of a novel breath test, that relies upon a unique panel of P. aeruginosa metabolic pathways to produce stable isotope labeled gasses from specific substrates. If successful, this work can be translated to provide a sensitive and rapid new diagnostic that could significantly improve management of this disease.